1. Field of the Invention
This invention relates to a fire control and navigational system for moving weapon carriers. More particularly, this invention pertains to such a system which is particularly suitable for battle tanks and other vehicles of the type that possess a primary and secondary-stabilized system movable relative to the vehicle.
2. Description of the Prior Art
In order to realize maximum usefulness, modern weapon systems must often be utilized in conjunction with moving weapon carriers. For weapons with a ballistic action, this requires some compensation of the various "disturbance variables" that occur when the projectile is fired. Accurate compensation requires knowledge of the movement of the weapon or, alternatively, stabilization of the weapon.
In a modern main battle tank, ballistic trajectories and ranges are determined by the elevation angle of the freely movable barrel. When a gun barrel that is movable about the vertical angle in azimuth and about an orthogonal axis in elevation is used with a moving vehicle, movement of the weapon carrier must be compensated to stabilize the weapon. Conventionally, the fire control system of a main battle tank is stabilized by employing several gyroscope sets as sensors for the primary stabilization of sighting means and the weapon system. Such a gyroscope set comprises, as a rule, two one degree-of-freedom rate gyroscopes that are mounted on the weapon. These serve to measure rotary movements about the elevation and azimuth axes and to compensate such movements by means of an associated closed loop control system employing servo drives. Additionally, the cant angle of the weapon must be detected by means of a perpendicularity sensor. Rate gyroscopes in the turret and hull prestabilize the weapon.
The battle tank as a directly aimed weapon possesses optical sights that enable the commander and gunner to detect target position. Once again, stabilization for use during travel is required in order that the weapon's line of sight may be stabilized. In the event that the sights are primary stabilized, such viewing devices must include two sets of uniaxial rate gyroscopes with appropriate servo-drives and control loops. This requires three primary-stabilized devices and, hence, six rate gyroscopes per tank. The rate gyroscopes are interactive; thus, when one gyroscope set fails, others are effected in their performances. Further, conventional gyroscopes often fail to provide guidance information, in the form of navigational data, in a suitable manner.
In a conventional main battle tank as described above, firing from a fast-moving weapon is accomplished only with reduced accuracy for a number of reasons. First, weapon movement cannot be completely known, as the aforementioned gyroscopes only measure rates of rotation. Translational movement of the weapon, for example, is not provided. (as shown in FIG. 1, the vehicle speed V.sub.F as well as the aiming speed V.sub.R (swing-angle speed W.sub.R) and the muzzle velocity V.sub.O of the projective are superimposed; thus, actual projectile velocity V.sub.G is obtained.)
Secondly, stabilization is conventionally carried out only as a directional stabilization. That is, the weapon's direction vector is maintained independent of the rates of rotation of the weapon carrier that occur. This phenomenon is illustrated in FIG. 2, a conceptual illustration of the weapon aiming process for a directionally stabilized (positive azimuth angle) gun barrel on a vehicle travelling over uneven terrain. Thus, the weapon may be stabilized directionally in space although with a parallel displacement. Depending on the direction of travel of the weapon carrier and target, relatively large translational displacements can occur that cannot be compensated by the stabilizing system alone.
Third, translational displacements can be compensated by the use of so-called auxiliary aiming aids and dynamic lead prediction wherein the gunner presets the aiming speed used by the fire control system for lead computation. Unfortunately, the aiming-angle speed W.sub.RS contains components of both the speed of the weapon carrier W.sub.Y and the speed of the target V.sub.F (see FIG. 3). The target speed must, however, be compensated according to the lead angle W.sub.V while the speed of the weapon carrier must be treated as a ballistic disturbance variable at the time the projectile is fired. Because two items of information are thus mixed in the aiming signal W.sub.RS, the weapon carrier must be stopped for a short time at the moment of firing to isolate the necessary information. Otherwise, a considerable burden is placed upon the gunner. Considerable experience is required to decide how accurately a projectile has struck a moving target when the weapon carrier is in motion. As a rule, dynamic lead predictions cannot be made correctly even when aided by auxiliary aiming aids.
Finally, the single axis rate gyroscopes often found in present-day weapon stabilizing systems provide an analog output of generally inadequate bandwidth and stability. Consequently, it is almost impossible to use measured rates of rotation for other system functions.